Why the ECU cares about air temperature
Hot air is less dense than cold air, so the same manifold pressure carries less oxygen into the cylinder on a hot day or after a long boost run. The intake air temperature (IAT) sensor lets the ECU account for that. When Auto VE Air Temp Compensation is turned on in Fuel Tuning, the Nexus uses this reading in its volumetric efficiency math. It's also the input behind corrections like air temp fuel correction and air temp ignition correction.
Most IAT sensors are simple two-wire thermistors: one wire carries the signal to an analog input, and the other goes to signal ground.
Setting it up in NSP
| Node | What you set | Our advice |
|---|---|---|
| Intake Air Temperature | The sensor calibration. Use Load from File for a Haltech sensor, or type the values in. Save to File keeps a copy | Always load the file for Haltech sensors instead of typing a table by hand |
| Display | Warning Maximum (where gauges and bars turn to warning) and Display Maximum (where gauges end, and the highest value settings and tables can use) | Set Display Maximum high enough to cover your hottest heat-soak |
| Diagnostics | High and low voltage DTCs, plus minimum and maximum value DTCs, each with a severity that triggers an Engine Protection level | Turn on the voltage DTCs so an unplugged sensor is caught |
| Wiring | The input, the Input Type, and the pull-up | Any free AVI works for a sensor wired straight to the ECU |
Input Type: voltage or resistance
The Input Type decides whether the calibration table is entered as voltage or as resistance against temperature. Resistance is handy when your sensor's data sheet only gives ohms, which is common with OEM sensors. Changing it switches the calibration screen in the main node.
Pull-up
Enable the pull-up for a two-wire sensor. The thermistor needs that internal resistor to 5 V to create a voltage the ECU can measure. With it off, the reading is meaningless.
Thermocouples for extreme heat
A K-type thermocouple can be used instead. That suits high-power turbo builds without an intercooler, where intake temperatures well over 390°F (200°C) are normal and a regular thermistor would be out of its range.
Mount the sensor where it sees moving air after the intercooler, as close to the engine as practical, and away from hot metal that can heat-soak it. A sensor in a dead spot reads the pipe, not the air.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reads a fixed extreme value | Pull-up off, open circuit, or wrong input assigned |
| Reads a few degrees off everywhere | Wrong calibration loaded for the sensor |
| Climbs steadily at idle | Heat soak from the sensor's mounting location |
Need a sensor? Haltech's air temp sensors come in M14 small thread, 3/8 NPT large thread and 1/4 NPT versions. For outside air, see the ambient air temperature sensor.
